Image displaying method and image displaying device

ABSTRACT

When displaying an image with at least four primary colors mixed, there are provided a primary color B generating unit ( 1036 ) having, as an xy chromaticity, (x, y)=(0.150, 0.060) and generating a primary color B lowest in luminance, a primary color G generating unit ( 1038 ) having, as an xy chromaticity, (x, y)=(0.300, 0.600) and generating a primary color G highest in luminance, and a primary color R generating unit ( 1037 ) having, as an xy chromaticity, (x, y)=(0.640, 0.330) and generating a primary color R higher in luminance than the primary color B and lower in luminance than the primary color G, whereby it is possible to expand a color gamut while ensuring compatibility with 3-primary-color image signal by allowing three primary colors to agree with the primary color Rec. 709 of a standard display sRGB.

This application is a U.S. National Phase application of PCTInternational Application PCT/JP02/10991.

TECHNICAL FIELD

The present invention relates to image display methods for computerdisplays and image display devices receiving TV broadcasts using four ormore primary colors, and image display devices using these methods.

BACKGROUND ART

Cross-media systems, in which a variety of image apparatuses areconnected to an open system, are becoming very popular in response toadvances in digital image apparatuses and network technology centeringon the Internet. In open systems, image apparatuses and applicationsneed to have a common interface and establish a configuration with highversatility and extendibility. From the aspect of color reproduction, animage apparatus sending color information, i.e., a camera or scanner,needs to send accurate color information captured to the open system. Onthe other hand, an image apparatus receiving and displaying colorinformation, i.e., a display or printer, needs to display accurately thecolor information received. For example, even though the camera capturesaccurate color information, the color reproducibility of the entiresystem is degraded if the display can only display color informationinappropriately.

To solve the above point, the IEC (International Electro-technicalCommission) has established a standard, sRGB, for standard displays.This standard clearly defines the relation between RGB video signals andcolorimetric values by matching the chromaticity point of the three RGBprimary colors to the colorimetric parameter defined in Rec. 709 asrecommended by ITU-R (International Telecommunication Union RadioCommunication). Accordingly, displays complying with thisstandard-display standard can calorimetrically display the same colorsif the same RGB video signals are given. On the other hand, displays areoften used for video editing as well as viewing the images displayed.For example, displays are used for creating originals for catalogprints. Therefore, “sRGB display,” the standard display, which allowscolorimetrical control, is a key to color management including hardcopying such as printing.

However, the above conventional image display device has the followingdisadvantages. “Pointer color gamut” and “SOCS color gamut” aredatabases that contain the color distribution of typical reflectiveobjects in the natural world. These databases give a dynamic range ofcolorimetric value input to cameras, and also provide design referencesfor the color gamut of displays. In other words, the color gamutcovering at least the sum of “Pointer color gamut” and “SOCS colorgamut” [hereafter (Pointer+SOCS) gamut] is required for accuratelydisplaying the colors of naturally reflective objects.

FIG. 3A is a sectional view of a gamut solid in the CIELAB space andshows the relation between the color gamut of the sRGB display and the(Pointer+SOCS) color gamut, which is the database for color distributionof naturally reflective objects, on the plane a*-b* at equal luminanceL*=50. It is apparent from FIG. 3 that color gamut 2001 of the sRGBdisplay is smaller than color gamut 2002 of (Pointer+SOCS), indicatingthat the sRGB display cannot display certain naturally reflectiveobjects. Calculation of gamut volume in the CIELAB space reveals thatthe sRGB display covers about 76% of the (Pointer+SOCS) color gamut, andthus 24% of the (Pointer+SOCS) color gamut is not displayable on thesRGB display. Accordingly, even though the camera captures a preciseimage securing a wide dynamic range covering the color distribution of anaturally reflective object, about 24% of the precisely captured imageis not displayable on the sRGB display.

A conventional image device solving this disadvantage is disclosed, forexample, in the Japanese Patent Laid-open Application No. 2001-306023.FIG. 10 shows the conventional image display device disclosed in thislaid-open patent.

In FIG. 10, the image display device configures multiple pixels 36aligned in a matrix. These pixels consists of sub-pixel 36R for redlight, sub-pixel 36G for green light, sub-pixel 36B for blue light, andsub-pixel 36C emitting light of cyan, magenta, or yellow. This sub-pixel36C is specified as a point on the chromaticity diagram outside of atriangular region formed by linking points of red (R), green (G), andblue (B) on the chromaticity diagram shown in FIG. 11. The CMY in FIG.11 indicates cyan (C), magenta (M), and yellow (Y).

In the above conventional configuration, however, a color display rangechanges with luminance because no restriction on luminance is provided.This makes it difficult to secure compatibility with the sRGB displaywhen the fourth primary color is added.

More specifically, the shape and size of the color gamut of the displayare determined by the positions of the primary color points. Since thecolor space is three-dimensional, primary color points havethree-dimensional coordinates. In the case of the sRGB display, eachprimary color R (primary color red), primary color G (primary colorgreen), and primary color B (primary color blue) possessestwo-dimensional chromaticity coordinates (x, y) and one-dimensionalluminance Y The (Pointer+SOCS) color gamut is also a three-dimensionalsolid. In order to display the precise colors of naturally reflectiveobjects, two-dimensional chromaticity coordinates and one-dimensionalluminance of primary colors of the display need to be determined suchthat the color gamut solid of the display covers the (Pointer+SOCS)color gamut solid to the maximum extent possible.

DISCLOSURE OF INVENTION

One object of the present invention is to offer an image display devicethat has compatibility with existing sRGB displays but has a broadercolor gamut.

An image display method of the present invention involves an imagedisplay method employing lights of four or more primary colors. The xychromaticity and luminance ratio of primary color R, primary color G,and primary color B are the same as those of the sRGB display. Imagesare displayed by mixing these three primary color lights and a fourthprimary color light. The fourth primary color light is in the visibleregion on the xy chromaticity diagram, possesses xy chromaticity outsidethe triangular region formed by primary color R, primary color G, andprimary color B; and has luminance lower than that of primary color G.This makes it possible to maintain compatibility with the sRGB display,and also to broaden the color gamut.

Moreover, the image display method of the present invention employinglights of four or more primary colors is characterized as follows. Thelight of primary color B has the xy chromaticity of (x, y)=(0.150,0.060) and the lowest luminance. The light of primary color G has the xychromaticity of (x, y)=(0.300, 0.600) and the highest luminance. Thelight of primary color R has the xy chromaticity of (x, y)=(0.640,0.330) and luminance higher than primary color B and lower than primarycolor G. The light of the fourth primary color has the xy chromaticityin a visible region on the xy chromaticity diagram but out of thetriangular region formed by primary color R, primary color G, andprimary color B, and luminance lower than primary color G. The imagedisplay method of the present invention displays images by mixing atleast these three primary color lights and the fourth primary colorlight. This makes it possible to secure compatibility with the sRGBdisplay, and also to broaden the color gamut.

The fourth primary color in the image display method of the presentinvention has the xy chromaticity in the visible region between thehalf-line extending from primary color R to primary color G and thehalf-line extending from the primary color R to primary color B, and hasthe xy chromaticity but outside of the triangular region. This allowsthe color gamut to be broadened most efficiently when only one primarycolor is added.

Moreover, in the image display method of the present invention, thefourth primary color has the xy chromaticity of (x, y)=(0.046, 0.535).In addition, when luminance of primary color R, primary color G, primarycolor B, and the fourth primary color are normalized to 100, luminanceof primary color B is 6.78, luminance of primary color G is 56.25,luminance of primary color R is 25.25, and luminance of the fourthprimary color is 11.72. This allows to maintain compatibility with thesRGB display, and also to broaden the color gamut in green and blueregions.

The image display method of the present invention employs the spatialadditive mixture, superimposed additive mixture, or temporal additivemixture. In the spatial additive mixture, a pixel is configured byspatially adjoining four or more primary colors for mixing colors. Inthe superimposed additive mixture, a pixel is configured by spatiallysuperimposing four or more primary colors at the same position formixing colors. In the temporal additive mixture, a pixel is configuredby temporally dividing four or more primary colors and displaying themfor mixing colors.

The image display device of the present invention generates four or moreprimary colors, and includes an primary color R generating unit, primarycolor G generating unit, primary color B generating unit, fourth primarycolor generating unit, spatial modulation unit, and video light mixer.The primary color R generating unit, primary color G generating unit,and primary color B generating units generate lights of three primarycolors with the xy chromaticity and luminance ratio same as those of thesRGB display for primary color R, primary color G, and primary color B.The fourth primary color generating unit generates light of the fourthprimary color with the xy chromaticity in the visible region on the xychromaticity diagram but outside of the triangular region formed byprimary color R, primary color G, and primary color B, and luminancelower than primary color G. The spatial modulation unit provided foreach primary color modulates each primary color light from thegenerating units using input video signals for each primary color. Thevideo light mixer mixes video lights from the spatial modulation unit.This allows to maintain compatibility with the sRGB display, and also tobroaden the color gamut.

Still more, the image display device of the present invention generatesfour or more primary colors, and includes the primary color B generatingunit, primary color G generating unit, primary color R generating unit,fourth primary color generating unit, spatial modulation unit and videolight mixer. The primary color B generating unit generates light ofprimary color B with the xy chromaticity of (x, y)=(0.150, 0.060) andthe lowest luminance. The primary color G generating unit generateslight of primary color G with the xy chromaticity of (x, y)=(0.3000.600) and the highest luminance, and the primary color R generatingunit generates light of primary color R with the xy chromaticity of (x,y)=(0.640, 0.330) and luminance higher than primary color B and lowerthan primary color G. The fourth primary color generating unit generateslight of the fourth primary color with the xy chromaticity in thevisible region on the xy chromaticity diagram but outside of thetriangular region formed by primary color R, primary color G, andprimary color B, and luminance lower than primary color G. The spatialmodulation unit modulates primary color lights input from thesegenerating units using video signals for each primary color. The videolight mixer mixes video lights from the spatial modulation unit. Thisallows to maintain compatibility with the sRGB display, and also tobroaden the color gamut.

The fourth primary color generating unit in the image display device ofthe present invention generates the light having the xy chromaticitybetween the half line extending from primary color R to primary color Gand the half line extending from primary color R and primary color B inthe visible region on the xy chromaticity diagram but outside of thetriangular region. This enables to broaden the color gamut mosteffectively when only one primary color is added. The light generated inthe fourth primary color generating unit in the image display device ofthe present invention has the xy chromaticity of (x, y)=(0.046, 0.535).In addition, when luminance of lights generated in the primary color Rgenerating unit, primary color G generating unit, primary color Bgenerating unit, and fourth primary color generating unit are normalizedto 100, luminance of primary color B is 6.78, primary color G is 56.25,primary color R is 25.25, and the fourth primary color is 11.72. Thisallows to maintain compatibility with the sRGB display and also tobroaden the color gamut in the green and blue regions.

The image light mixer in the image display device of the presentinvention executes the spatial additive mixture, superimposed additivemixture, or temporal additive mixture. In the spatial additive mixture,a pixel is configured by spatially adjoining four or more primary colorsfor mixing colors. In the superimposed additive mixture, a pixel isconfigured by spatially superimposing four or more primary colors at thesame position for mixing colors. In the temporal additive mixture, apixel is configured by temporally dividing four or more primary colorsand displaying them for mixing colors.

The primary color generating units in the image display device of thepresent invention employs a dichroic mirror for spectrally reflecting apart of the light from the light source, and transmitting remaininglight so as to generate light of each primary color. This allowsgeneration of multiple primary colors based on light from the lightsource.

Still more, the primary color generating units in the image displaydevice of the present invention employs a filter for spectrallyabsorbing a part of the light from the light source and transmittingremaining light so as to generate light of each primary color. Thisallows generation of multiple primary colors based on light from thelight source.

The image display device of the present invention includes a lightsource directly or indirectly emitting the light, liquid crystal panelfor modulating the light from the light source using input videosignals, and a color filter panel. The color filter panel outputs lightof each primary color modulated using spectral transmittance to achievethe next xy chromaticity coordinates: (x, y)=(0.150, 0.060) for primarycolor B, (x, y)=(0.300, 0.600) for primary color G, (x, y)=(0.640,0.330) for primary color R, and (x, y)=(0.046, 0.535) for the fourthprimary color. This allows to maintain compatibility with the sRGBdisplay and also to broaden the color gamut.

The image display device of the present invention further includes ascaling circuit for scaling three-primary video signals for the sRGBdisplay. When the fourth primary color video signal is not input, thesignal from this scaling circuit is output to the spatial modulationunit. Accordingly, conversion with the sRGB display is simply done byscaling, facilitating the manufacture of a display specifying thechromaticity and luminance of four primary colors.

As described above, the present invention offers an image display devicewhich maintains compatibility with existing sRGB displays and has abroader color gamut three-dimensionally by employing four or moreprimary colors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration of an image display system in accordance witha first exemplary embodiment of the present invention.

FIG. 2 is a configuration of a 4-primary color image display device inaccordance with the first exemplary embodiment of the present invention.

FIG. 3A is a sectional view of a color gamut in the CIELAB spacetypically of a conventional sRGB display

FIG. 3B is a sectional view of a color gamut in the CIELAB spacetypically of the 4-primary color display in accordance with the firstexemplary embodiment of the present invention.

FIG. 4 is a chromaticity diagram indicating the color gamut of the sRGBdisplay and the color gamut of the 4-primary color display in accordancewith the first exemplary embodiment of the present invention.

FIG. 5 illustrates the relation among primary colors, secondary colors,tertiary colors, black, and white in accordance with the first exemplaryembodiment of the present invention.

FIG. 6 is a configuration of a driving circuit of the video displaysystem in accordance with the first exemplary embodiment of the presentinvention.

FIG. 7 is a configuration of a driving circuit using matrix calculationcircuit in accordance with the first exemplary embodiment.

FIG. 8 is a configuration of a 4-primary color image display device inaccordance with a second exemplary embodiment of the present invention.

FIG. 9 is a configuration of a 5-primary color image display device inaccordance with a third exemplary embodiment of the present invention.

FIG. 10 is a pixel in a conventional image display device.

FIG. 11 is a chromaticity diagram for the conventional image displaydevice.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)

Exemplary embodiments of the present invention are described below withreference to the drawings.

The exemplary embodiments use primary color C (cyan primary color) asthe fourth primary color in the description.

First Exemplary Embodiment

FIG. 1 shows a configuration of an image display system in a firstexemplary embodiment of the present invention.

In FIG. 1, driving circuit 101 is a circuit for generating a modulationelement driving signal for displaying images when a video input signalis input. Image display device 102 creates all the RGBC primary colorlights from light source 103, and supplies them to spatial modulationelements respectively, and video lights modulated by the modulationelement driving signal are synthesized and then output for display.

FIG. 2 is an example of the configuration of an image display devicehaving four primary colors (hereafter referred to as a “4-primary colordisplay”).

Light 1002 from light source 1001 enters first dichroic mirror 1003 inprimary color B generating unit 1036, and the short wavelengthcomponents are reflected here so as to generate B-primary color light1004. B-primary color light 1004 is generated in a way such that its xychromaticity becomes (x, y)=(0.150, 0.060). If the xy chromaticitycannot be adjusted simply by the reflection characteristics of firstdichroic mirror 1003, B-primary color adjustment filter 1020 is used foradjusting its spectral characteristics.

B-primary color light 1004 then enters B-primary color spatialmodulation element 1005 controlled by B-primary color video signal 1101,and video tone information is added so as to modulate to B-channel videolight 1006.

Light 1007 passing through first dichroic mirror 1003 enters seconddichroic mirror 1008 in primary color R generating unit 1037, and longwavelength components are reflected here so as to generate R-primarycolor light 1009. R-primary color light 1009 is generated in a way suchthat its xy chromaticity becomes (x, y)=(0.300, 0.600). If the xychromaticity cannot be adjusted simply by the reflection characteristicsof second dichroic mirror 1008, R-primary color adjustment filter 1021is used for adjusting its spectral characteristics.

R-primary color light 1009 then enters R-primary color spatialmodulation element 1010 controlled by R-primary color video signal 1102,and video tone information is added so as to modulate to R-channel videolight 1011.

Light 1012 passing through second dichroic mirror 1008 enters thirddichroic mirror 1013 in primary color G generating unit 1038, and thelong wavelength components are reflected here so as to generateG-primary color light 1014. G-primary color light 1014 is generated in away such that its xy chromaticity becomes (x, y)=(0.640, 0.330). If thexy chromaticity cannot be adjusted simply by the reflectioncharacteristics of third dichroic mirror 1013, G-primary coloradjustment filter 1022 is used for adjusting its spectralcharacteristics.

G-primary color light 1014 then enters G-primary color spatialmodulation element 1015 controlled by G-primary color video signal 1103,and video tone information is added so as to modulate to G-channel videolight 1016.

Light passing through third dichroic mirror 1013 enters primary color Cgenerating unit 1039, and C-primary color light 1017 is generated.C-primary color light 1017 is generated in a way such that its xychromaticity becomes (x, y)=(0.046, 0.535). If the xy chromaticitycannot be adjusted simply by the transmission characteristics of thirddichroic mirror 1013, C-primary color adjustment filter 1023 is used foradjusting its spectral characteristics.

C-primary color light 1017 then enters C-primary color spatialmodulation element 1018 controlled by C-primary color video signal 1104,and video tone information is added so as to modulate to C-channel videolight 1019.

Video light mixer 1035 mixes B-channel video light 1006, R-channel videolight 1011, G-channel video light 1016, and C-channel video light 1019using reflective mirror 1030 and half-mirrors 1032 to 1034. A mixedvideo light is displayed on screen 1040. Colors are mixed based onspatial additive mixture, superimposed additive mixture, or temporaladditive mixture. In these processes, colors are mixed by composing apixel by spatially adjoining four or more primary colors, spatiallysuperimposing the positions of four or more primary colors, ortemporally dividing four or more primary colors for display.

B-primary color ND filter 1024, R-primary color ND filter 1025,G-primary color ND filter 1026, and C-primary color ND filter 1027adjust only the light intensity of lights emitted from B-primary coloradjustment filter 1020, R-primary color adjustment filter 1021,G-primary color adjustment filter 1022, and C-primary color adjustmentfilter 1023 without changing their spectral characteristics. Throughthis adjustment, the luminance of the lights emitted from each ND filteris adjusted to the following values when the sum of luminance of lightsemitted from ND filters is 100: 6.78 for the light emitted fromB-primary color ND filter 1024, 25.25 for the light emitted fromR-primary color ND filter 1025, 56.25 for the light emitted fromG-primary color ND filter 1026, and 11.72 for the light emitted fromC-primary color ND filter 1027.

B-primary color spatial modulation element 1005, R-primary color spatialmodulation element 1010, G-primary color spatial modulation element1015, and C-primary color spatial modulation element 1018 are equivalentto the spatial modulation unit.

B-primary color video signal 1101, R-primary color video signal 1102,G-primary color video signal 1103, and C-primary color video signal 1104are equivalent to the modulation element driving signal shown in FIG. 1.

FIG. 3B is a sectional view illustrating a color gamut in the CIELABspace of the 4-primary color display in the first exemplary embodiment.The color gamut is cut by a uniform plane at L*=50 in CIELAB space. Itcan be noted that color gamut 2001 of the sRGB display is a part ofcolor gamut 3001 of the 4-primary color display. This happens becauseB-primary color light 1004, R-primary color light 1009, and G-primarycolor light 1014 conform to the RGB primary colors of the sRGB display.

The 4-primary color display in FIG. 2 further has C-primary color light1017 as the fourth primary color. It can be noted that the color gamutspreads widely over a region from green to blue by setting the xychromaticity point of this color to (x, y)=(0.046, 0.535). When colorgamut 3001 of the 4-primary color display is compared with color gamut2002 of the (Pointer+SOCS) color gamut, which is the color distributiondatabase for naturally reflective objects, (Pointer+SOCS) color gamut2002 is completely covered in the green and blue region which cannot becovered by the sRGB display, but (Pointer+SOCs) color gamut 2002 isbroader in part of the orange to yellow region. Therefore, it can beunderstood that the 4-primary color display mostly covers color gamut2002 of (pointer+SOCS) color gamut and also color gamut 2001 of the sRGBdisplay.

Next, colors are projected on a chromaticity diagram, ignoringbrightness information, for identifying the entire color gamut.

FIG. 4 is an xy chromaticity diagram for the 4-primary color display inthe first exemplary embodiment.

In FIG. 4, horseshoe shape 4007 is the visible region, and B-primarycolor 4001 is (x, y)=(0.150, 0.060), G-primary color 4002 is (x,y)=(0.300, 0.600), R-primary color 4003 is (x, y)=(0.640, 0.330), andC-primary color 4004 is (x, y=(0.046, 0.535). Accordingly, B-primarycolor 4001, G-primary color 4002, and R-primary color 4003 conform toRec. 709, and triangle 4005 formed by these colors is the color gamut ofthe sRGB display. Triangle 4006 formed by C-primary color 4004,B-primary color 4001, and G-primary color 4002 is the color gamutextended by introducing the fourth primary color C. In other words, thedisplay range has broadened for colors given names such as blue,blue-green, and green. In particular, the color gamut can be extendedmost efficiently by selecting the fourth primary color in an areasurround by four points that are crossing point 4008 of theextended-line from R-primary color 4003 to G-primary color 4002 andhorseshoe shape 4007, crossing point 4009 of the half-line fromR-primary color 4003 to B-primary color 4001 and horseshoe shape 4007,B-primary color 4001, and G-primary color 4002.

The color gamut formed by four primary colors: B-primary color 4001,G-primary color 4002, R-primary color 4003, and C-primary color 4004covers 95% of the (Pointer+SOCS) color gamut for naturally reflectiveobjects. The coverage by color gamut 4005 of the sRGB display is 76%. Itis apparent that introduction of C-primary color 4004 has significantlybroadened the color gamut of the 4-primary color display.

The color distribution of naturally reflective objects and the coverageof the color gamut of the 4-primary color display are described below.

Pointer gamut data base (Color Research and Application) and SOCS gamutdatabase (ISO) are valid for the color distribution of naturallyreflective objects. The Pointer gamut database gives CIELAB values orCIELUV values using standard light C as a reference white color. TheSOCS gamut database gives spectral reflectance factors. Values in theSOCS gamut database are combined with values in the Pointer gamutdatabase, and they are converted to CIELAB values. Naturally reflectiveobjects are distributed in a closed region including the achromaticcolor axis. Accordingly, if the color gamut of the display can coverthis closed region, any color of naturally reflective objects can bereproduced on the display.

The color gamut of the display can be defined based on the tristimulusvalue XYZ of four primary colors. More specifically, the color gamut ofthe display is a solid formed by 14 points consisting of four primarycolors (B, C, G, and R) called primary colors, colors made by addingprimary colors (B+C, C+G, G+R, R+B) called secondary colors, colors madeby adding secondary colors (B+C+G, C+G+R, G+R+B, R+B+C) called tertiarycolors, and black and white (W=B+C+G+R) as shown in FIG. 5. The coveragerelation of the above two color gamuts can be identified by cutting thissolid of the display color gamut along the L*uniform plane, as shown inFIG. 3B, and comparing with the color distribution of naturallyreflective objects.

The relation between the xy chromaticity and XYZ tristimulus value isexpressed by Equation 1.

$\begin{matrix}{\begin{bmatrix}X \\Y \\Z\end{bmatrix} = \begin{bmatrix}{\frac{x}{y}Y} \\{\frac{1 - x - y}{y}Y}\end{bmatrix}} & (1)\end{matrix}$

Luminance Y of four primary color points is a relative value normalizedto 100: 6.78 for B-primary color, 56.25 for G-primary color, 25.25 forR-primary color, and 11.72 for C-primary color. Accordingly, tristimulusvalue XYZ of four primary colors is (X, Y, Z)=(16.94, 6.78, 89.24) forB-primary color, (X, Y, Z)=(28.13, 56.25, 9.38) for G-primary color, (X,Y, Z)=(48.97, 25.25, 2.30) for R-primary color, and (X, Y, Z)=(1.00,11.72, 9.17) for C-primary color.

Next, compatibility between the 3-primary color system and 4-primarycolor system is described.

By matching the chromaticity coordinates of three primary colors, i.e.,primary color R, primary color G, and primary color B, out of fourprimary colors to Rec. 709; two advantages are achieved as follows.

The first advantage is that the display design can be simplified. Inother words, three-color materials used in conventional RGB 3-primarycolor displays can be utilized to produce three colors in four primarycolors. Since the chromaticity coordinates of primary color B, primarycolor G, and primary color R are the same, with only luminance Ydiffering, the 4-primary color display can set primary color B, primarycolor G, and primary color R simply by adjusting the gain usingB-primary color ND filter 1024, R-primary color ND filter 1025, andG-primary color ND filter 1026 as shown in FIG. 2. If, for example, thechromaticity coordinates for primary color B, primary color G, andprimary color R are set to other than the chromaticity coordinates inRec. 709, the materials for all four primary colors would need to bere-designed for the 4-primary color display. Accordingly, the use ofconventional Rec. 709 primary colors gives a broader set of advantageswith respect to development period, reliability, development cost, etc.

The second advantage is the compatibility of the video interface. In thecase of the 4-primary color display, four types of video signals, i.e.,R_(d4), G_(d4), B_(d4), and C_(d4), are input. If xy chromaticitycoordinates of primary colors corresponding to three video signalsR_(d4), G_(d4), and B_(d4) conform to Rec. 709, compatibility with videosignals for the 3-primary color display is achieved by introducing ascaling circuit. In the case of the 3-primary color display, videosignals R_(d3)′, G_(d3)′, and B_(d3)′ linear to luminance Y after CRTgamma correction are converted to display colors [X_(d3), Y_(d3),Z_(d3)]^(t) on the display by Equation 2.

where

$\begin{matrix}{\begin{bmatrix}X_{d3} \\Y_{d3} \\Z_{d3}\end{bmatrix} = {\begin{bmatrix}X_{R3} & X_{G3} & X_{B3} \\Y_{R3} & Y_{G3} & Y_{B3} \\Z_{R3} & Z_{G3} & Z_{B3}\end{bmatrix}\begin{bmatrix}R_{{d3}^{\prime}} \\G_{{d3}^{\prime}} \\B_{{d3}^{\prime}}\end{bmatrix}}} & (2)\end{matrix}$

[X_(b3), Y_(B3), Z_(B3)]^(t) is tristimulus value XYZ of primary colorB;

[X_(G3), Y_(G3), Z_(G3)]^(t) is tristimulus value XYZ of primary colorG; and

[X_(R3), Y_(R3), Z_(R3)]^(t) is tristimulus value XYZ of primary colorR.

Equation 3 below is obtained by rewriting Equation 2 using Equation 1.

$\begin{matrix}{\begin{bmatrix}X_{d3} \\Y_{d3} \\Z_{d3}\end{bmatrix} = {\begin{bmatrix}{\frac{x_{R3}}{y_{R3}}Y_{R3}} & {\frac{x_{G3}}{y_{G3}}Y_{G3}} & {\frac{x_{B3}}{y_{B3}}Y_{B3}} \\Y_{R3} & Y_{G3} & Y_{B3} \\{\frac{1 - x_{R3} - y_{R3}}{y_{R3}}Y_{R3}} & {\frac{1 - x_{G3} - y_{G3}}{y_{G3}}Y_{G3}} & {\frac{1 - x_{B3} - y_{B3}}{y_{B3}}Y_{B3}}\end{bmatrix}\begin{bmatrix}R_{{d3}^{\prime}} \\G_{{d3}^{\prime}} \\B_{{d3}^{\prime}}\end{bmatrix}}} & (3) \\{{{{Where}\mspace{461mu}\begin{bmatrix}X_{d3} \\Y_{d3} \\Z_{d3}\end{bmatrix}} = {\begin{bmatrix}X_{R3} & X_{G3} & X_{B3} \\Y_{R3} & Y_{G3} & Y_{B3} \\Z_{R3} & Z_{G3} & Z_{B3}\end{bmatrix}\begin{bmatrix}R_{{d3}^{\prime}} \\G_{{d3}^{\prime}} \\B_{{d3}^{\prime}}\end{bmatrix}}}\mspace{140mu}} & (2)\end{matrix}$

x_(B3), y_(B3), z_(B3) are chromaticity coordinates xyz of primary colorB;

x_(G3), y_(G3), z_(G3) are chromaticity coordinates xyz of primary colorG; and

x_(R3), y_(R3), z_(R3) are chromaticity coordinates xyz of primary colorR.

In case of the 4-primary color display, video signals R_(d4)′, G_(d4)′,B_(d4)′, and C_(d4)′ linear to luminance Y after CRT gamma correctionare converted to display colors [X_(d4) Y_(d4) Z_(d4)]^(t) on thedisplay by Equation 4.

$\begin{matrix}{\begin{bmatrix}X_{d4} \\Y_{d4} \\Z_{d4}\end{bmatrix} = {\begin{bmatrix}X_{R4} & X_{G4} & X_{B4} & X_{C4} \\Y_{R4} & Y_{G4} & Y_{B4} & Y_{C4} \\Z_{R4} & Z_{G4} & Z_{B4} & Z_{C4}\end{bmatrix}\begin{bmatrix}R_{{d4}^{\prime}} \\G_{{d4}^{\prime}} \\B_{{d4}^{\prime}} \\C_{{d4}^{\prime}}\end{bmatrix}}} & (4)\end{matrix}$

Where

[X_(B4) Y_(B4) Z_(B4)]^(t) is tristimulus value XYZ of primary color B;

[X_(G4) Y_(G4) Z_(G4)]^(t) is tristimulus value XYZ of primary color G;

[X_(R4) Y_(BR) Z_(R4)]^(t) is tristimulus value XYZ of primary color R;

[X_(C4) Y_(C4) Z_(C4)]^(t) is tristimulus value XYZ of primary color C.

Equation 5 below is obtained by rewriting Equation 4 using Equation 1.

$\begin{matrix}{{{\begin{bmatrix}X_{d4} \\Y_{d4} \\Z_{d4}\end{bmatrix} = \begin{bmatrix}{\frac{x_{R4}}{y_{R4}}Y_{R4}} & {\frac{x_{G4}}{y_{G3}}Y_{G4}} & {\frac{x_{B4}}{y_{B4}}Y_{B4}} & {\frac{x_{C4}}{y_{C4}}Y_{C4}} \\Y_{R4} & Y_{G4} & Y_{B4} & Y_{C4} \\{\frac{1 - x_{R4} - y_{R4}}{y_{R4}}Y_{R4}} & {\frac{1 - x_{G4} - y_{G4}}{y_{G4}}Y_{G4}} & {\frac{1 - x_{B4} - y_{B4}}{y_{B4}}Y_{B4}} & \frac{1 - x_{C4} - y_{C4}}{y_{C4}}\end{bmatrix}}\quad}\begin{bmatrix}R_{{d4}^{\prime}} \\G_{{d4}^{\prime}} \\B_{{d4}^{\prime}} \\C_{{d4}^{\prime}}\end{bmatrix}} & (5)\end{matrix}$

Where,

x_(B4), y_(B4), z_(B4) are chromaticity coordinates xyz of primary colorB;

x_(G4), y_(G4), z_(G4) are chromaticity coordinates xyz of primary colorG;

x_(R4), y_(R4), z_(R4) are chromaticity coordinates xyz of primary colorR; and

x_(C4), y_(C4), z_(C4) are chromaticity coordinates xyz of primary colorC.

If the chromaticity coordinates of primary color B, primary color G, andprimary color R of the 4-primary color display match those of primarycolor B, primary color G, and primary color R of the 3-primary colordisplay, Equations 3 and 5 can be expressed by Equation 6 at the sametime as follows.

$\begin{matrix}{\begin{bmatrix}X_{d4} \\Y_{d4} \\Z_{d4}\end{bmatrix} = {\begin{bmatrix}{\frac{x_{R3}}{y_{R3}}Y_{R4}} & {\frac{x_{G3}}{y_{G3}}Y_{G4}} & {\frac{x_{B3}}{y_{B3}}Y_{B4}} & {\frac{x_{C4}}{y_{C4}}Y_{C4}} \\Y_{R4} & Y_{G4} & Y_{B4} & Y_{C4} \\{\frac{1 - x_{R3} - y_{R3}}{y_{R3}}Y_{R4}} & {\frac{1 - x_{G3} - y_{G3}}{y_{G3}}Y_{G4}} & {\frac{1 - x_{B3} - y_{B3}}{y_{B3}}Y_{B4}} & \frac{1 - x_{C4} - y_{C4}}{y_{C4}}\end{bmatrix}\begin{bmatrix}{w_{R}R_{{d4}^{\prime}}} \\{w_{G}G_{{d4}^{\prime}}} \\{w_{B}B_{{d4}^{\prime}}} \\{w_{C}C_{{d4}^{\prime}}}\end{bmatrix}}} & (6) \\{w_{R} = \left\{ \begin{matrix}\frac{Y_{R3}}{Y_{R4}} & \left( {C_{d\; 4^{\prime}} \neq 0} \right) \\1 & \left( {C_{d\; 4^{\prime}} = 0} \right)\end{matrix} \right.} & \; \\{w_{G} = \left\{ \begin{matrix}\frac{Y_{G3}}{Y_{G4}} & \left( {C_{d\; 4^{\prime}} \neq 0} \right) \\1 & \left( {C_{d\; 4^{\prime}} = 0} \right)\end{matrix} \right.} & \; \\{w_{B} = \left\{ \begin{matrix}\frac{Y_{B3}}{Y_{B4}} & \left( {C_{d\; 4^{\prime}} \neq 0} \right) \\1 & \left( {C_{d\; 4^{\prime}} = 0} \right)\end{matrix} \right.} & \; \\{w_{C} = \left\{ \begin{matrix}\frac{Y_{\;{C3}}}{Y_{C4}} & \left( {C_{d\; 4^{\prime}} \neq 0} \right) \\{arbitrary} & \left( {C_{d\; 4^{\prime}} = 0} \right)\end{matrix} \right.} & \;\end{matrix}$

In other words, when video signals R_(d3)′, G_(d3)′, and B_(d3)′ for the3-primary color display are input, involvement of primary color to thedisplay color is shut off by w_(c)=0. Moreover, a difference inluminance of primary color B, primary color G, and primary color R canbe absorbed by w_(R), w_(G), and w_(B).

FIG. 6 shows the configuration of driving circuit 101 in the imagedisplay device corresponding to Equation 6.

In FIG. 6, the 4-primary color display is configured by video interface6001 and processing circuit 6002. R-channel image signal 6003, G-channelimage signal 6004, B-channel image signal 6005, and C-channel videosignal 6006 are input to processing circuit 6002 from video interface6001, and video signals are converted to luminance linear signals R′,G′, B′, and C′ in degamma circuits 6007 to 6010 respectively for eachchannel. Signal C is input to C-signal detector 6011 for detecting thepresence of C-channel video signal 6006. If C-channel video signal 6006is detected (including C=0), C-signal detector 6011 gives an instructionto scaling circuits 6012 to 6014 respectively for R channel, G channeland B channel to send signal R′, signal G′, and signal B′ respectivelyto spatial modulation element driving circuits 6015 to 6017 withoutscaling because C-channel video signal 6006 is a signal for the4-primary color display. At the same time, signal C′ is sent fromC-primary color degamma circuit to C-primary color spatial modulationelement driving circuit 6018 so as to display images using the mixtureof four primary colors on the 4-primary color display.

If no C-channel video signal 6006 is input when RGB signals for the3-primary color display are input to video interface 6001 as R-channelimage signal 6003, G-channel image signal 6004, and B-channel imagesignal 6005; C-signal detector 6011 detects the absence of C-channelvideo signal 6006, and gives an instruction to scaling circuits 6012 to6014 to execute scaling. In accordance with this instruction, R-primarycolor scaling circuit 6012 executes scaling equivalent to w_(R) inEquation 6. In the same way, G-primary color scaling circuit 6013executes scaling equivalent to w_(G) in Equation 6, and B-primary colorscaling circuit 6014 executes scaling equivalent to w_(B) in Equation 6.Accordingly, signals are converted to driving signals for the 3-primarycolor display, and then they are sent to respective spatial modulationelement driving circuits 6015 to 6017.

Since no C-channel video signal 6006 is input, no signal is input toC-primary color spatial modulation element driving circuit 6018.Accordingly, lights for C-primary color in image display device 103 areall extinguished by C-primary color spatial modulation element, and animage using a mixture of three primary colors RGB is displayed.

If chromaticity of primary colors is not specified as (x, y)=(0.150,0.60) for primary color B, (x, y)=(0.300, 0.600) for primary color G,(x, y)=(0.640, 0.330) for primary color R, and (x, y)=(0.046, 0.535) forprimary color C in the CIELAB space at L*=50 as in the prior art, andthe chromaticity coordinates do not conform to Rec. 709, it is necessaryto convert to R′, G′, and B′ signals for the 4-primary color displaywhich are colorimetrically equivalent to sRGB signals by sRGB inputs.

First, the colorimetric values [X_(d3) Y_(d3) Z_(d3)]^(t) of displaycolors of sRGB signals, which are input signals, are given by Equation3. Then, calculation is implemented using the chromaticity coordinatesof RGB primary color points conforming to Rec. 709[R-primary color(x_(R3), y_(R3))=(0.0640, 0.330), G-primary color (x_(G3),y_(G3))=(0.300, 0.600), and B-primary color (x_(B3), y_(B3))=(0.150,0.060)] and relative luminance (Y_(R3) Y_(G3) Y_(B3))=(21.25, 71.54,7.21).

Colorimetric value [X_(d4) Y_(d4) Z_(d4)]^(t) of display colors by RGBprimary colors excluding primary color C in the 4-pirmary color displayis given by Equation 7.

$\begin{matrix}{\mspace{11mu}{\begin{bmatrix}X_{d4} \\Y_{d4} \\Z_{d4}\end{bmatrix}\mspace{655mu}\mspace{11mu}{\quad{\begin{bmatrix}{\frac{x_{R4}}{y_{R4}}Y_{R4}} & {\frac{x_{G4}}{y_{G4}}Y_{G4}} & {\frac{x_{B4}}{y_{B4}}Y_{B4}} \\Y_{R4} & Y_{G4} & Y_{B4} \\{\frac{1 - x_{R4} - y_{R4}}{y_{R4}}Y_{R4}} & {\frac{1 - x_{G4} - y_{G4}}{y_{G4}}Y_{G4}} & {\frac{1 - x_{B4} - y_{B4}}{y_{B4}}Y_{B4}}\end{bmatrix}\mspace{95mu}\begin{bmatrix}R_{{d4}^{\prime}} \\G_{{d4}^{\prime}} \\B_{{d4}^{\prime}}\end{bmatrix}}\mspace{650mu}}}} & (7)\end{matrix}$

R′ G′, and B′ signals for the 4-primary display colorimetricallyequivalent to input sRGB signals are given by Equation 8 as follows.

$\begin{matrix}\begin{matrix}{{\begin{bmatrix}X_{d4} \\Y_{d4} \\Z_{d4}\end{bmatrix}\; = \begin{bmatrix}X_{d3} \\Y_{d3} \\Z_{d3}\end{bmatrix}}\;} \\\left. \Leftrightarrow{\quad\begin{bmatrix}{\frac{x_{R4}}{y_{R4}}Y_{R4}} & {\frac{x_{G4}}{y_{G4}}Y_{G4}} & {\frac{x_{B4}}{y_{B4}}Y_{B4}} \\Y_{R4} & Y_{G4} & Y_{B4} \\{\frac{1 - x_{R4} - y_{R4}}{y_{R4}}Y_{R4}} & {\frac{1 - x_{G4} - y_{G4}}{y_{G4}}Y_{G4}} & {\frac{1 - x_{B4} - y_{B4}}{y_{B4}}Y_{B4}}\end{bmatrix}} \right. \\{\begin{bmatrix}R_{{d4}^{\prime}} \\G_{{d4}^{\prime}} \\B_{{d4}^{\prime}}\end{bmatrix}\;} \\{= {\quad\begin{bmatrix}{\frac{x_{R3}}{y_{R3}}Y_{R3}} & {\frac{x_{G3}}{y_{G3}}Y_{G3}} & {\frac{x_{B3}}{y_{B3}}Y_{B3}} \\Y_{R3} & Y_{G3} & Y_{B3} \\{\frac{1 - x_{R3} - y_{R3}}{y_{R3}}Y_{R3}} & {\frac{1 - x_{G3} - y_{G3}}{y_{G3}}Y_{G3}} & {\frac{1 - x_{B3} - y_{B3}}{y_{B3}}Y_{B3}}\end{bmatrix}}} \\{\begin{bmatrix}R_{{d3}^{\prime}} \\G_{{d3}^{\prime}} \\B_{{d3}^{\prime}}\end{bmatrix}\;} \\{{\left. \Leftrightarrow{M_{{d4},}{{RGB}\begin{bmatrix}R_{{d4}^{\prime}} \\G_{{d4}^{\prime}} \\B_{{d4}^{\prime}}\end{bmatrix}}} \right.\; = {M_{d3}\begin{bmatrix}R_{{d3}^{\prime}} \\G_{{d3}^{\prime}} \\B_{{d3}^{\prime}}\end{bmatrix}}}\;} \\{{{\left. \Leftrightarrow\begin{bmatrix}R_{{d4}^{\prime}} \\G_{{d4}^{\prime}} \\B_{{d4}^{\prime}}\end{bmatrix} \right.\; = {M^{- 1}{d4}}},{{RGB}\;{M_{d3}\begin{bmatrix}R_{{d3}^{\prime}} \\G_{{d3}^{\prime}} \\B_{{d3}^{\prime}}\end{bmatrix}}}}\;}\end{matrix} & (8)\end{matrix}$

FIG. 7 shows the configuration of a driving circuit for the 4-primarycolor display when the chromaticity coordinates of primary color R,primary color G, and primary color B is not matched to Rec. 709.

A point different from the driving circuit for the 4-primary colordisplay when the chromaticity coordinates of R-primary color, G-primarycolor, and B-primary color conform to Rec. 709 is that matrixcalculation circuit 7001 is needed instead of the scaling circuit foreach of the RGB primary colors. This matrix calculation circuitcalculates 3 lines and 3 rows in matrix as shown in Equation 8.Therefore, the matrix calculation circuit is larger and more expensivethan the scaling circuit.

As described above, the 4-primary color display in the first exemplaryembodiment matches the chromaticity coordinates of primary color R,primary color G, and primary color B to Rec. 709, and identifiesone-dimensional luminance Y. This allows the use of materials for theconventional RGB 3-primary display. In addition, the driving circuit canuse a simple scaling calculation for securing compatibility with3-primary color video signals. Accordingly, a 4-primary color displayfor a broad color gamut that covers most of the color distribution ofnaturally reflective objects is achievable.

The configuration shown in FIG. 2 is suitable for a projector, anddemonstrates the capability to display an image closer to the actualimage when the image is reproduced on a large screen at the size of theoriginal.

It is apparent that the present invention does not apply restrictions tothe sequence of generating each primary color. In other words, thesequence of generating each primary color can be determined as required.

Second Exemplary Embodiment

FIG. 8 is the configuration of a 4-primary color liquid crystal displayin a second exemplary embodiment of the present invention.

In FIG. 8, the light emitted from light source 8001 is reflected onreflector 8002, and enters liquid crystal panel 8003. Liquid crystalpanel 8003 is demodulated by the operation of liquid crystal paneldriving circuit 8005 driven by a video signal given by video memory8004, and video tone is expressed as light intensity. The light passingthrough liquid crystal panel 8003 enters color filter panel 8006, andspectral energy distribution is changed and output based on the opticalabsorption characteristic of the colored material.

Color filter panel 8007, which is a fragmentary magnified view to showthe structure of color filter panel 8006, consists of four colorfilters: B-filter 8008, G-filter 8009, R-filter 8010, and C-filter 8011.These four color filters are disposed in units of 2×2 cells. The videosignal is sent to this 2×2 cell as one pixel. Since there are fourprimary colors, a “square pixel” required for the computer display iseasily made feasible.

As shown in FIG. 4, the four primary colors B, G, R, and C havechromaticity coordinates identical to those in the first exemplaryembodiment: (x, y)=(0.150, 0.060) for primary color B, (x, y)=(0.300,0.600) for primary color G, (x, y)=(0.640, 0.330) for primary color R,and (x, y)=(0.046, 0.535) for primary color C. If the size of each colorfilter is sufficiently small beyond the limit of visible resolution,lights passing each color filter are mixed, and the color gamutcombining triangle 4005 and triangle 4006 is achieved.

As described above, the liquid crystal display in the second exemplaryembodiment also conforms the chromaticity coordinates of primary colorR, primary color G, and primary color B to Rec. 709, as in the firstexemplary embodiment, and identifies one-dimensional luminance Y.Accordingly, materials for the conventional RGB 3-primary color liquidcrystal display can be used, and the driving circuit can use a simplescaling calculation for securing compatibility with 3-primary colorvideo signals. A 4-primary color display with a broad color gamut mostlycovering the color distribution of naturally reflective objects can thusbe achieved.

The configuration in the second exemplary embodiment is suitable for adesktop display, and is effective in displaying video images closer tothe real image for editing texts in desktop publishing (DTP).

It is noted that the present invention does not place restrictions onthe spatial positions of the color filters. Positions for B-filter 8008,G-filter 8009, R-filter 8010, and C-filter 8011 in FIG. 8 are determinedas required.

Third Exemplary Embodiment

FIG. 9 is the configuration of a liquid crystal display having fiveprimary colors in a third exemplary embodiment of the present invention.

Color filter panel 9006 is different from the liquid crystal display ofthe second exemplary embodiment in FIG. 8.

Color filter 9007, which is a fragmentary magnified view of color filterpanel 9006, consists of five color filters as one pixel: B-filter 9008,G-filter 9009, R-filter 9010, C1-filter 9011, and C2-filter 9012. As inthe second exemplary embodiment, the spectral transmittance is designedsuch that lights passing B-filter 9008, G-filter 9009, and R-filter 9010have chromaticity coordinates conforming to Rec. 709 for primary colorB, primary color G, and primary color R. Primary color C1 and primarycolor C2 act in the same way as C-primary color 4004, and are arrangedin regions given names such as blue, blue green, and green, contributingto broadening of the color gamut.

This configuration requires the development of only two new materialsfor primary color C1 and primary color C2 in the 5-primary colordisplay, and achieves compatibility with the 3-primary color videosignal same as in the first exemplary embodiment.

As described above, the liquid crystal display in the third exemplaryembodiment also conforms the chromaticity coordinates for primary colorR, primary color G, and primary color G to Rec. 709, as in the firstexemplary embodiment, and identifies one-dimensional luminance YAccordingly, materials for the conventional RGB 3-primary color liquidcrystal display can be used, and the driving circuit can use a simplescaling calculation for securing compatibility with 3-primary colorvideo signals. A 5-primary color display with a broad color gamut mostlycovering the color distribution of naturally reflective objects can thusbe achieved.

It is noted that the present invention does not place restrictions onthe spatial positions of the color filters. Positions for B-filter 9008,G-filter 9009, R-filter 9010, C1-filter 9011, and C2-filter 9012 in FIG.9 are determined as required.

INDUSTRIAL APPLICABILITY

As described above, the present invention is effective for image displaydevices employing four or more primary colors. The present inventionsecures compatibility with conventional sRGB displays and is suitablefor displaying in a precise fashion the colors of naturally reflectiveobjects.

Reference numerals in the drawings  36 Pixel 36R, 36G, 36B, 36CSub-pixel  101 Driving circuit  102 Image display device  103 Lightsource 1001 Light source 1002 Light from light source 1003 Firstdichroic mirror 1004 B-primary color light 1005 B-primary color spatialmodulation element 1006 B-channel video light 1007 Light passing throughfirst dichroic mirror 1003 1008 Second dichroic mirror 1009 R-primarycolor light 1010 R-primary color spatial modulation element 1011R-channel video light 1012 Light passing through second dichroic mirror1008 1013 Third dichroic mirror 1014 G-primary color light 1015G-primary color spatial modulation element 1016 G-channel video light1017 Light passing through third dichroic mirror 1013 1018 C-primarycolor spatial modulation element 1019 C-channel video light 1020B-primary color adjustment filter 1021 R-primary color adjustment filter1022 G-primary color adjustment filter 1023 C-primary color adjustmentfilter 1024 B-primary color ND filter 1025 R-primary color ND filter1026 G-primary color ND filter 1027 C-primary color ND filter 1030, 1031Reflective mirror 1032, 1033, 1034 Half mirror 1035 Video light mixer1036 Primary color B generating unit 1037 Primary color R generatingunit 1038 Primary color G generating unit 1039 Primary color Cgenerating unit 1040 Screen 2001 Color gamut of sRGB display 2002(Pointer + SOCS) color gamut 2003 Visible region 3001 Color gamut of4-primary color display 4001 B-primary color 4002 G-primary color 4003R-primary color 4004 C-primary color 6001 Video interface of 4-primarycolor display 6002 Processing circuit of 4-primary color display 6003R-channel image signal 6004 G-channel image signal 6005 B-channel imagesignal 6006 C-channel image signal 7001 Matrix calculation circuit 8001Light source 8002 Reflector 8003 Liquid crystal panel 8004 Video memory8005 Liquid crystal panel driving circuit 8006 Color filter panel 8007Magnified view of color filter panel 8006 8008 B-filter 8009 G-filter8010 R-filter 8011 C-filter 9006 Color filter panel 9007 Magnified viewof color filter panel 9006 9008 B-filter 9009 G-filter 9010 R-filter9011 C1-filter 9012 C2-filter

1. An image display method employing lights of four or more primary colors, said method displaying an image by at least mixing: lights of three primary colors having xy chromaticity and luminance ratio of primary color R, primary color G, and primary color B same as those of an sRGB display; and light of a fourth primary color having xy chromaticity in a visible region on an xy chromaticity diagram but outside a triangular region formed by said primary color R, said primary color G, and said primary color B; and luminance lower than said primary color G.
 2. The image display method as defined in claim 1, wherein xy chromaticity of said fourth primary color is located in said visible region between a half line extending from said primary color it to said primary color G and a half line extending from said primary color R and primary color B, but outside said triangular region.
 3. The image display method as defined in claim 2, wherein xy chromaticity of said fourth primary color is (x, y)=(0.046, 0.535); and luminance normalized to 100 of said primary color R, said primary color G, said primary color B, and said fourth primary color are: 6.78 for luminance of said primary color B, 56.25 for luminance of said primary color G, 25.25 for luminance of said primary color R, and 11.72 for luminance of said fourth primary color.
 4. The image display method as defined in claim 3, wherein said mixing is one of spatial additive mixture, superimposed additive mixture, and temporal additive mixture.
 5. The image display method as defined in claim 2, wherein said mixing is one of spatial additive mixture, superimposed additive mixture, and temporal additive mixture.
 6. An image display method employing lights of four or more primary colors, said method displaying an image by at least mixing: light of primary color B having xy chromaticity of (x, y)=(0.150, 0.060) and lowest luminance; light of primary color G having xy chromaticity of (x, y)=(0.300, 0.600) and highest luminance; light of primary color R having xy chromaticity of (x, y)=(0.640), 0.330) and luminance higher than said primary color B and lower than said primary color G; and light of a fourth primary color having xy chromaticity in a visible region on an xy chromaticity diagram but outside a triangular region formed by said primary color R, said primary color G, and said primary color B; and luminance lower than said primary color G.
 7. The image display method as defined in claim 2, wherein xy chromaticity of said fourth primary color is located in said visible region between a half line extending from said primary color R to said primary color G and a half line extending from said primary color R and primary color B, but outside said triangular region.
 8. The image display method as defined in claim 7, wherein said mixing is one of spatial additive mixture, superimposed additive mixture, and temporal additive mixture.
 9. An image display device for generating four or more primary colors, said device comprising: a primary color R generating unit, primary color G generating unit, and primary color B generating unit for generating lights of three primary colors with xy chromaticity and luminance ratio or primary color R, primary color G, and primary color B same as those of an sRGB display; a fourth primary color generating unit for generating light of a fourth primary color having xy chromaticity in a visible region on an xy chromaticity diagram but outside a triangular region formed by said primary color R, said primary color G, and said primary color B; and luminance lower than said primary color G; a spatial modulation unit for each primary color, said spatial modulation unit modulating each primary color light from said primary color R generating unit, said primary color G generating unit, said primary color B generating unit, and said fourth primary color generating unit by an input video signal for each primary color; and a video light mixer for mixing each video light from said spatial modulation unit.
 10. The image display device as defined in claim 9, wherein said fourth primary color generating unit generates light having xy chromaticity in said visible region between a half line extending from said primary color R to said primary color G and a half line extending from said primary color R to said primary color B, but outside said triangular region.
 11. The image display device as defined in claim 10, wherein said light generated in said fourth primary color generating unit has xy chromaticity of (x, y)=(0.046, 0.535); and luminance normalized to 100 of lights generated in said primary color R generating unit, said primary color G generating unit, said primary color B generating unit, and said fourth primary color generating unit is: 6.78 for luminance of said primary color B, 56.25 for luminance of said primary color G, 25.25 for luminance of said primary color R, and 11.72 for luminance of said fourth primary color.
 12. The image display device as defined in claim 11, wherein said video light mixer executes one of spatial additive mixture, superimposed additive mixture, and temporal additive mixture.
 13. The image display device as defined in claim 12, wherein said generating unit for each primary color generates light of each primary color using a dichroic mirror to reflect a part of light from a light source spectrally and pass through remaining light.
 14. The image display device as defined in claim 12, wherein said generating unit for each primary color generates light of each primary color using a filter to absorb a part of light from a light source spectrally and pass through remaining light.
 15. The image display device as defined in claim 11, wherein said generating unit for each primary color generates light of each primary color using a dichroic mirror to reflect a part of light from a light source spectrally and pass through remaining light.
 16. The image display device as defined in claim 11, wherein said generating unit for each primary color generates light of each primary color using a filter to absorb a part of light from a light source spectrally and pass through remaining light.
 17. The image display device as defined in claim 11 further comprising a scaling circuit for scaling three-primary color video signals for an sRGB display, said scaling circuit outputting a signal to said spatial modulation unit when no video signal for said fourth primary color is input.
 18. The image display device as defined in claim 10, wherein said video light mixer executes one of spatial additive mixture, superimposed additive mixture, and temporal additive mixture.
 19. The image display device as defined in claim 18, wherein said generating unit for each primary color generates light of each primary color using a dichroic mirror to reflect a part of light from a light source spectrally and pass through remaining light.
 20. The image display device as defined in claim 18, wherein said generating unit for each primary color generates light of each primary color using a filter to absorb a part of light from a light source spectrally and pass through remaining light.
 21. The image display device as defined in claim 10, wherein said generating unit for each primary color generates light of each primary color using a dichroic mirror to reflect a part of light from a light source spectrally and pass through remaining light.
 22. The image display device as defined in claim 10, wherein said generating unit for each primary color generates light of each primary color using a filter to absorb a part of light from a light source spectrally and pass through remaining light.
 23. The image display device as defined in claim 10 further comprising a scaling circuit for scaling three-primary color video signals for an sRGB display, said scaling circuit outputting a signal to said spatial modulation unit when no video signal for said fourth primary color is input.
 24. The image display device as defined claim 9, wherein said generating unit for each primary color generates light of each primary color using a dichroic mirror to reflect a part of light from a light source spectrally and pass through remaining light.
 25. The image display device as defined in claim 9, wherein said generating unit for each primary color generates light of each primary color using a filter to absorb a part of light from a light source spectrally and pass through remaining light.
 26. The image display device as defined in claim 9, further comprising a scaling circuit for scaling three-primary color video signals for an sRGB display, said sealing circuit outputting a signal to said spatial modulation unit when no video signal for said fourth primary color is input.
 27. An image display device for generating at least four primary colors, said device comprising: a primary color B generating unit for generating light of primary color B having xy chromaticity of (x, y)=(0.150, 0.060) and lowest luminance; a primary color G generating unit for generating light of primary color G having xy chromaticity of (x, y)=(0.300, 0.600) and highest luminance; a primary color R generating unit for generating light of primary color R having xy chromaticity of(x, y)=(0.640, 0.330) and luminance higher than said primary color B and lower than said primary color G; a fourth primary color generating unit for generating light of a fourth primary color having xy chromaticity in a visible region on an xy chromaticity diagram but outside a triangular region formed by said primary color R, said primary color G, and said primary color B; and luminance lower than said primary color G; a spatial modulation unit for each primary color, said spatial modulation unit modulating each primary color light from said primary color R generating unit, said primary color G generating unit, said primary color B generating unit, and said fourth primary color generating unit by an input video signal for each primary color; and a video light mixer for mixing each video light from said spatial modulation unit.
 28. The image display device as defined in claim 27, wherein said fourth primary color generating unit generates light having xy chromaticity in said visible region between a half line extending from said primary color R to said primary color G and a half line extending from said primary color R to said primary color B, but outside said triangular region.
 29. The image display device as defined in claim 28, wherein said light generated in said fourth primary color generating unit has xy chromaticity of (x, y)=0.046, 0.535); and luminance normalized to 100 of lights generated in said primary color R generating unit, said primary color G generating unit, said primary color B generating unit, and said fourth primary color generating unit is: 6.78 for luminance of said primary color B, 56.25 for luminance of said primary color G, 25.25 for luminance of said primary color R, and 11.72 for luminance of said fourth primary color.
 30. The image display device as defined in claim 29, wherein said video light mixer executes one of spatial additive mixture, superimposed additive mixture, and temporal additive mixture.
 31. The image display device as defined in claim 30, wherein said generating unit for each primary color generates light of each primary color using a dichroic mirror to reflect a part of light from a light source spectrally and pass through remaining light.
 32. The image display device as defined in claim 30, wherein said generating unit for each primary color generates light of each primary color using a filter to absorb a port of light from a light source spectrally and pass through remaining light.
 33. The image display device as defined in claim 29, wherein said generating unit for each primary color generates light of each primary color using a dichroic mirror to reflect a part of light from a light source spectrally and pass through remaining light.
 34. The image display device as defined in claim 29, wherein said generating unit for each primary color generates light of each primary color using a filter to absorb a part of light from a light source spectrally and pass through remaining light.
 35. The image display device as defined in claim 29 further comprising a scaling circuit far scaling three-primary color video signals for an sRGB display, said scaling circuit outputting a signal to said spatial modulation unit when no video signal for said fourth primary color is input.
 36. The image display device as defined in claim 28, wherein said video light mixer executes one of spatial additive mixture, superimposed additive mixture, and temporal additive mixture.
 37. The image display device as defined in claim 36, wherein said generating unit for each primary color generates light of each primary color using a dichroic mirror to reflect a part of light from a light source spectrally and pass through remaining light.
 38. The image display device as defined in claim 36, wherein said generating unit for each primary color generates light of each primary color using a filter to absorb a part of light from a light source spectrally and pass through remaining light.
 39. The image display device as defined in claim 28, wherein said generating unit for each primary color generates light of each primary color using a dichroic mirror to reflect a part of light from a light source spectrally and pass through remaining light.
 40. The image display device as defined in claim 28, wherein said generating unit for each primary color generates light of each primary color using a filter to absorb a part of light from a light source spectrally and pass through remaining light.
 41. The image display device as defined in claim 28 further comprising a scaling circuit for scaling three-primary color video signals for an sRGB display, said scaling circuit outputting a signal to said spatial modulation unit when no video signal for said fourth primary, color is input.
 42. The image display device as defined in claim 27, wherein said generating unit for each primary color generates light of each primary color using a dichroic mirror to reflect a part of light from a light source spectrally and pass through remaining light.
 43. The image display device as defined in claim 27, wherein said generating unit for each primary color generates light of each primary color using a filter to absorb a part of light from a light source spectrally and pass through remaining light.
 44. The image display device as defined in claim 27 further comprising a scaling circuit for scaling three-primary color video signals for an sRGB display, said scaling circuit outputting a signal to said spatial modulation unit when no video signal for said fourth primary color is input. 